Treating Challenging Wastewaters with Ceramic Membranes

While polymeric membranes are used extensively for treating domestic and industrial wastewaters, ceramic membranes have some unique characteristics that make them uniquely suitable for processing challenging waters. Their biggest advantage in these applications is their higher chemical resistance, enabling them to be cleaned more effectively and reducing the chance of irreversible fouling. An example of this is the Shibaura WWTP in Tokyo, Japan, which has been operating for the last 11 years with a small residual of ozone in the secondary effluent going to the membranes; the 0.3 mg/L O3 (average) dosage enables fluxes of up to 135 gallons per square foot of membrane area per day (gfd), and reduces chemically-enhanced backwashes (CEBs) to 10 mg/L NaOCl every 3-7 days and clean-in-place (CIP) cleanings to every 60 days. Another feature of ceramic membranes that makes them well-suited for treating challenging wastewaters is their higher hydrophilicity (affinity for water), which minimizes fouling. An example of this is in the treatment of flowback water, the wastewater produced through hydraulic fracturing – “fracking. A Houston-based oil company partnered with Aqua-Aerobic Systems (Aqua) to design, manufacture, and commission a 6,000 barrels per day (bbl/day) mobile ceramic membrane system for use at their wells in western Texas. The system operated at 6 – 8 psi transmembrane pressure (TMP) and removed over 98% of the hydrocarbons, iron, and suspended solids. Treatment of this wastewater would have been difficult with polymeric membranes because their lower hydrophilicity would cause increased hydrocarbon fouling. A third feature of ceramic membranes that is especially applicable to wastewater reuse is their integrity: to achieve the required pathogen removal, polymeric membranes often require frequent repair (pinning) and replacement, while ceramic membranes do not. Because of this, the Terminal Island WWTP piloted the Aqua ceramic membrane system to determine the viability of replacing the existing system with one containing more-durable membranes. The pilot treated both tertiary and secondary effluent from the plant, with and without coagulant pretreatment. Once optimized, the pilot was able to maintain stable operation treating secondary effluent containing 4.2 mg/L Al+3 at a flux of 100 gfd, over 3 times the flux of the current polymeric membranes! In addition, the pilot operated at around 97% recovery.

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